Design Doc: Lambda Annotation

[normj]

The AWS .NET team is working on a new library for constructing .NET Lambda functions. The design doc can be viewed and commented on in this PR #961.

The high level overview of the new library is to use .NET source generator support to translating from the low level single event object programming model of Lambda to an experience similar to ASP.NET Core but with minimal overhead. The initial work is focused on REST API Lambda functions but the technology is applicable for other Lambda event types.

For example developers will be able to write a Lambda function like the following with the ICalculator service being injected by dependency injection and and the LambdaFunction and HttpApi attributes directing the source generator to generator the compatible Lambda boiler plate code and sync with the CloudFormation template.

public class Functions
{
	ICalculator _calulator;

	public Functions(ICalculator calculator)
	{
		_calulator = calculator;
	}

	[LambdaFunction]
	[HttpApi(HttpMethod.Get, HttpApiVersion.V2, "/add/{x}/{y}")]
	public int Add(int x, int y)
	{
		return _calulator.Add(x, y);
	}
}

We would appreciate feedback on the design. What use cases what you like this library to help solve and what boiler plate code can we remove from your applications to make it simple to write Lambda functions.

---

Update 12/21/2021

We are excited to announce that Lambda Annotations first preview is here. Developers using the preview version of Amazon.Lambda.Annotations NuGet package can start using the simplified programming model to write REST and HTTP API Lambda functions on .NET 6. (Only Image package type is supported as of now)

Example (sample project)

[LambdaFunction(Name = "CalculatorAdd", PackageType = LambdaPackageType.Image)]
[RestApi(HttpMethod.Get, "/Calculator/Add/{x}/{y}")]
public int Add(int x, int y, [FromServices]ICalculatorService calculatorService)
{
    return calculatorService.Add(x, y);
}

[LambdaStartup]
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddScoped<ICalculatorService, CalculatorService>();
    }
}

Learn more about the Lambda Annotations and supported feature set here.

We cannot overstate how critical your feedback is as we move forward in the development. Let us know your experience working with Lambda Annotations in GitHub issues.

[CalvinAllen]

Dependency Injection is a huge plus, to me. I've had to roll that myself to support it - same with logging and configuration / environmental configuration.

EDIT: Why confused, @normj ?

[Lanayx]

Source generators is not dotnet, but csharp technology, so will be applicable only to csharp, with fsharp it won't be usable.

[mtschneiders]

Would it also generate the code needed for manual invocation via Lambda Test Tool?

 public static async Task Main()
  {
      var func = new Startup().FunctionHandler;
      using var handlerWrapper = HandlerWrapper.GetHandlerWrapper(func, new DefaultLambdaJsonSerializer());
      using var bootstrap = new LambdaBootstrap(handlerWrapper);
      await bootstrap.RunAsync();
  }

[normj]

Dependency Injection is a huge plus, to me. I've had to roll that myself to support it - same with logging and configuration / environmental configuration.

EDIT: Why confused, @normj ?

@CalvinAllen Sorry clicked the wrong emoji

[CalvinAllen]

@normj Ha, okay. I was a little confused myself, trying to figure out what I said, lol.

[Kralizek]

It would be great to see more of the plumbing, which happened to be the weakest point of Lambda development.

As @CalvinAllen wrote, logging, configuration and service registration are all concerns that required some time to work in a vanilla function.

But I generally love the idea of seeing multi-function packages becoming first class citizen of the new toolkit.

[petarrepac]

why is this being introduced ?
what problems it solves ?
what are expected benefits over the current approach?
what are the downsides ?

[normj]

why is this being introduced ? what problems it solves ? what are expected benefits over the current approach? what are the downsides ?

@petarrepac Are you saying these questions are not answered in the design doc?